1. Field of the Invention
This invention generally relates to communications networks and more particularly to networks having routers and circuit switches.
2. Description of the Related Art
It is well known for routers of messages (in a packet-switched network) to communicate with one another in accordance with the Open Shortest Path First (“OSPF”) protocol, which is governed by a standard of the Internet Engineering Task Force (“IETF”). IETF document RFC 1583 (“IETF RFC 1583”), shown in Appendix G, describes OSPF Version 2 and is incorporated herein by reference in its entirety. IETF documents in general, including RFC 1583, are available at the IETF Internet web site. In OSPF, messages containing information about the location of various routers and interconnections among the routers (also called “network topology”) are sent by the routers to one another. Each router maintains and updates a database of network topology information retrieved from such messages, which are also called “Link State Advertisements” (“LSA”). Each router uses the network topology information to determine the shortest path from itself to all other routers in the network.
The OSPF protocol has been enhanced to support a new class of LSA messages called “Opaque LSAs.” Opaque LSAs are described in IETF RFC 2370, shown in Appendix H and incorporated herein by reference in its entirety. Opaque LSAs consist of a conventional LSA header followed by an information field that may be used directly by OSPF or by other applications. Implementation of Opaque LSAs provides an application interface for 1) encapsulating application-specific information in a specific opaque type, 2) sending and receiving application-specific information, and 3) if required, informing the application of the change in validity of previously received information when topological changes are detected.